Nitrate leaching from temperate perennial pastures grazed by dairy cows in south-eastern Australia
R. J. Eckard A B , R. E. White A , R. Edis A , A. Smith A and D. F. Chapman AA Institute of Land and Food Resources, The University of Melbourne, Parkville, Vic. 3010, Australia.
B Corresponding author; email: rjeckard@unimelb.edu.au
Australian Journal of Agricultural Research 55(9) 911-920 https://doi.org/10.1071/AR04042
Submitted: 18 February 2004 Accepted: 15 July 2004 Published: 24 September 2004
Abstract
Nitrate (NO3-N) leaching losses were measured over 3 years from a temperate grass/clover pasture with and without 200 kg N fertiliser/ha, applied as ammonium nitrate or urea, using a system of moles and tile drains. Fertiliser was applied in 4 split dressings of 50 kg N/ha in each of the 4 seasons of each year. Drainage was collected continuously and NO3-N concentrations in drainage water were measured in subsamples collected using a flow-proportioned sampler. Pastures were rotationally grazed with dairy cows at stocking rates equivalent to 1.9 or 2.8 cows/ha for the unfertilised and fertilised treatments, respectively.
Soil water deficit (SWD) varied markedly between seasons and years, with drainage occurring in the cooler, wetter months (April–October) and not at all through the summer. There were no significant differences between treatments in SWD, drainage events, or drainage volumes.
Peak NO3-N concentrations were 19, 50, and 17 mg/L for the control, ammonium nitrate, and urea treatments, respectively. Mean annual flow-weighted NO3-N concentrations over the 3 years were 1.7 and 2.2 times higher from the ammonium nitrate treatment than from the urea and control treatments, respectively. Annual NO3-N leaching loads (kg N/ha) were 3.7–14.6 from the control treatment, 6.2– 22.0 from the urea treatment, and 4.3–37.6 from the ammonium nitrate treatment, for the lowest and highest drainage years, respectively.
The experiment confirmed that the application of N fertiliser prior to periods of substantial drainage can result in high losses of NO3-N through leaching. More efficient and environmentally sound use of N fertiliser can be achieved by not combining high N fertiliser rates, high stocking intensity, and nitrate-containing fertilisers prior to periods when there is a risk of substantial drainage occurring.
Additional keywords: ammonium nitrate, mole drain, nitrate concentration, nitrate loads, soil water deficit, urea, water balance.
Acknowledgments
The authors acknowledge the support of the Victorian Department of Primary Industries, the University of Melbourne, the Australian Research Council (grant no. C19804739), Dairy Australia, and Incitec Pivot Ltd for financing the study. In particular the authors thank Paul Durling for technical support.
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